Canted magnetic field for calutron ion source

ABSTRACT

In a calutron-type ion source, enhanced ion production and extraction are accomplished by orienting the ionizing electron beam in a nonparallel relationship to the arc slit from which the ions are extracted. This may be accomplished by canting the ion source a few degrees with respect to the magnetic field that confines the ionized beam or, preferably, by positioning the ion source conventionally and canting the magnetic field with respect to it.

United States Patent William A. Bell, Jr.;

Allen M. Veach, both 01 Oak Ridge, Tenn. 885,790

Dec. 17, 1969 Oct. 5, 1971 The United States of America as represented by the United States Atomic Energy Commission Inventors Appl. No. Filed Patented Assignee CAN'I'ED MAGNETIC FIELD FOR CALUTRON ION SOURCE 4 Claims, 1 Drawing Fig.

u.s. Cl 50 4195 1, 250/419 c Int. Cl n01 j 39/34 Field of Search 250/419 c,

41.9 SA,41.9 SR;313/63 I [56] I References Cited UNITED STATES PATENTS 2,715,693 8/1955 MacNeille 8t 31 313/63 2,715,695 8/1955 De .luren 313/63 2,882,409 4/1959 Lawrence 250/419 Primary Examiner-William F. Lindquist ArlorneyRoland A. Anderson ABSTRACT: In a calutron-type ion source, enhanced ion production and extraction are accomplished by orienting the ionizing electron beam in a nonparallel relationship to the arc slit from which the ions are extracted. This may be accomplished by canting the ion source a few degrees with respect to the magnetic field that confines the ionized beam or, preferably, by positioning the ion source conventionally and canting the magnetic field with respect to it.

PATENTEUUCT SIB?! 3,610,923

Km V/////////////\ v D, INVENTORS.

'" William A.BeH, Jr.

BY Allen M. Veach BACKGROUND OF THE INVENTION This invention was made in the course of, or under, a contract with the U.S. Atomic Energy Commission.

The field of art to which the present invention pertains is that involving calutrons for the electromagnetic isotopic separation of the ionic species of various elements. It has been one of the aims in the prior calutron art to provide the ion source of the calutron with means for producing more intense ion beams. The grid ion source of U. S. Pat. No. 2,933,630 to John S. Luce, issued Apr. l9, I960, and of U.S. Pat. No. 2,926,25l to John S. Luce et al., issued Feb. 23, I960, produced such ion beams. However, the grid ion source has actually been utilized only in lithium isotope separations. The high angular divergence (sidewise spread) of the ion beam caused unfocusable beams for other elements.

A more successful technique was that of positioning the ionizing electron beam defining slot closer to the arc slit of the ion source. In this arrangement, the defining slot was positioned one thirty'second inch or closer to the are slit. However, even this arrangement had certain disadvantages. For example, the are was unable, are conditions were critical and sensitive, and any sudden drain changes grosly defocused the beam, such that very careful operating conditions had to be maintained to achieve proper operation of the calutron.

Underlying the above and other developments of the prior art is a relationship that was considered to be basic prior to the present invention. It is that the magnetic field that confines the ionizing beam of electrons (are column) is aligned parallel with the ion extraction slit of the calutron ion source, and all prior calutrons were constructed incorporating the above relationship.

The present invention utilizes a different relationship between the above components of the calutron ion source in a manner to be discussed hereinbelow, such that the calutron can be operated in a more efficient manner to produce an increased ion output therefrom than that which is possible with prior art calutrons, and, at the same time, providing more stable operation of the calutron.

SUMMARY OF THE INVENTION It is the object of the present invention to provide an improved calutron wherein the calutron may be operated in a more efficient manner and to produce an ion output therefrom which is increased above that which was previously achievable.

The above object has been accomplished in the present invention by modifying the ion source of a calutron in such a manner that the ionizing electron beam of the source is oriented in a nonparallel relationship with respect to the arc slit of the source from which the ions are extracted. This may be accomplished by canting the ion source a few degrees with respect to the magnetic field that confines the ionizing beam or, preferably, by positioning the ion source conventionally and canting the magnetic field with respect to it. In addition, the height of the electron beam defining slot is made taller than the height of the ion extraction (arc) slit, such that the arc column (electron beam) finds its anode on the inside of the arc chamber above and below the ion extraction slit. It has been determined that a calutron with the above modifications to the ion source thereof, during a typical separation run, provides about 10 percent more useable ion output than the 1/32- inch technique mentioned hereinabove.

BRIEF DESCRIPTION OF THE DRAWING oEscRlr'rioN OF THE PREFERRED EMBODIMENT,

Only the necessary portions of the improved ion source of a calutron system are shown in the single FIGURE of the drawing for an understanding of the present invention. It should be understood that the ion source of the present invention may be utilized in a complete calutron system such as disclosed in U.S. Pat. No. 2,709,222 to E. 0. Lawrence, to which reference is made. It should also be understood that the necessary charge vapor for the ion source of the present invention is supplied to the ion source in a conventional manner. One means for heating the charge material for use in the ion source is disclosed in U.S. Pat. No. 3,] [5,575 to W. A. Bell et al., to which reference is made.

In the single FIGURE of the drawing, the conventional parts of a typical ion source are as follows: are chamber 15, cathode I7, arc'defining slot 18, accelerating electrode 27, decelerating electrode 29, ion-extracting (arc) slit 31, are chamber cover 33, and calutron tank walls 35. In order to provide for orientation of the electron (are) beam 23 of the ion source in a nonparallel relationship with respect to the ion extraction slit 31 in accordance with the present invention, two angled faces 20 and 20 are cut in otherwise conventional magnet shims l9 and 19'. These faces are parallel with respect to each other and are cut at an angle that will tilt the magnetic field H the desired amount. It should be noted in the figure that the front edge of the arc column 23 just contacts the inside edge of ion extraction slit 3] on the cathode side and the rear edge of arc column 23 shaves the outside edge of slit 3! on the opposite side. Accordingly, arc column 23 finds its anode above and below the ion extraction slit 31, with the arc column extending along the length of the slit, rather than finding its anode at conventional point 37 as in the prior art. This is done, with the aid of the tilted magnetic field, by making the height of the arc-defining slit 18 greater than the height of the are slit 31.

In the ion source, illustrated in the single FIGURE in the drawing, the calutron tank is about 13 inches across in the arc chamber region and the above-mentioned tilt is one-fourth inch in 13 inches which is also the ofi'set at which the shims l9 and 19' were cut, such that the magnetic field H is tilted in this amount. The height of the ion extraction slit 3i is seven thirtyseconds inch and it is about 5 inches long, while the height of the arc-defining slot 18 is about one-half inch, which is not drawn to scale in the drawing. The front edge of the slot 18 is one thirty-second inch from the arc chamber cover 33.

It should be understood that the above-mentioned amount of tilt is not critical but is given by way of example only. The above-described ion source has been utilized in a calutron system employing other conventional components such as an oven for vaporizing a charge material which is fed into the arc chamber of the ion source in a conventional manner as in the above-mentioned Bell et al. patent and an ion receiver, wherein sulfur, tellurium, and boron isotope separations were performed. Some of the results are shown in the following table.

TABLE Isotope Sulfur-33 Tellurium-123 Boron-10 Feed material COS Te Metal CaFz.BF;i or 1301 Shims t Tilted Standard Tllted Standard Tilted Standard Number of runs, averaged 14 7 2 3 12 14 Total run, hurs 462 458 40 54 242 194 Peak ion current (ma 130. 4 111. 4 71 56 74. 4 59. 7 Average ion current (ma 94.5 92.0 51.5 47.5 40.9 28.5 Charge consumption rate (g r.) 0.78 l. 0 .457 .35 Process eflfieieney (material collected] material used, percent). 4.3 10.8 3. 33 3.03

From the above table it can be seen that where the tilted This invention has been described by way of illustration shims were used there was an increase in peak ion current and average ion current as compared to the calutron runs where standard shims were utilized. In addition, there was an increase in process efficiency for the isotope separations involving the sulfur and boron when the tilted shims were utilized. The data on process efficiency for the isotope separations involving tellurium were inadvertently not calculated and are not now available, but it can be assumed that there was indeed an increase thereof since the peak ion current and average ion current were increased when the tilted shims were used.

The above results have been further demonstrated by some sulfur isotope separation runs that were performed in a calutron tank, during which several of the following modifications were tried, without success. During the series of runs, it was attempted to operate the calutron without an arc chamber cover, and it was not possible to sustain an electron arc (the arc column) across the arc chamber. Also, it was attempted to operate the calutron with the height of the arc-defining slot 18 of the ion source equal to the height of the ion extraction slit 31. Again, an arc could not be maintained. It was concluded that the arc column anodes on the back of the arc chamber cover. Therefore, the defining slot height was made greater than the ion extraction slit height with the proportions set forth hereinabove, such that substantially stable operation of the calutron was achieved.

it may be noted from the above table that the average ion current for sulfur is less improved than in the tellurium and boron runs. This is probably the result of difficulty in maintaining a steady arc of sulfur. This difficulty can be alleviated by providing a magnetic field tilt slightly less than that specified hereinabove such that the arc will be improved and bring the average ion current up.

it should be noted that the present invention has been prac ticed in another way. Instead of altering the shims, the arc chamber and electrodes were angled the desired amount in the calutron tank. It was found that the tilt was so small that the receiver could be properly positioned to receive the ion beam from the ion source. The output from this type of operation was similarly improved over the prior art to substantially the same degree as was the case for the tilted shim embodiment described hereinabove.

It should be understood that the present invention is not limited to the isotope separations specifically mentioned hereinabove but is equally applicable to substantially all other separations.

rather than limitation and it should be apparent that it is equally applicable in fields other than those described.

What is claimed is:

1. In a calutron system including an ion source chamber provided with a chamber cover having a narrow elongated ion exit slit, said chamber adapted to receive a vaporized charge material therein, means for producing an arc discharge which is associated with and passes through said chamber by means of an arc-defining slot for ionizing the charge material within said chamber, a magnetic field for effecting charge separation of the ions as they pass from said ion source exit slit, and accelerating means mounted adjacent to said ion exit slit for accelerating ions exited from said ion source, the improvement comprising means for slightly canting the direction of the magnetic field with respect to the direction of the elongated face portion of the ion exit slit of said ion source chamber cover such that said are discharge contacts the chamber inside edge of the ion exit slit on the discharge cathode side and the rear edge of said are discharge shaves the outside edge of the other end of said exit slit, whereby the stability of said are discharge is substantially improved and the useable ion output of said source is increased.

2. The calutron set forth in claim I, wherein said means for slightly canting said ma netic field with respect to the direction of the elongate portion of said ion exit slit com- 3. The calutron set forth in claim I, wherein said means for slightly canting the direction of said magnetic field with respect to the direction of the elongated face portion of said ion exit slit comprises providing a pair of spaced-apart magnetic shims between which said ion source chamber is mounted in spaced relation thereto, each of said shims having its face adjacent to said ion source cut at an angle such that said angled faces are parallel with respect to each other to provide a selected tilt to the direction of said magnetic field with respect to the direction of the elongated face portion of said ion source exit slit.

4. The calutron set forth in claim 3, wherein said tilt is about one-fourth inch in 13 inches. 

1. In a calutron system including an ion source chamber provided with a chamber cover having a narrow elongated ion exit slit, said chamber adapted to receive a vaporized charge material therein, means for producing an arc discharge which is associated with and passes through said chamber by means of an arc-defining slot for ionizing the charge material within said chamber, a magnetic field for effecting charge separation of the ions as they pass from said ion source exit slit, and accelerating means mounted adjacent to said ion exit slit for accelerating ions exited from said ion source, the improvement comprising means for slightly canting the direction of the magnetic field with respect to the direction of the elongated face portion of the ion exit slit of said ion source chamber cover such that said arc discharge contacts the chamber inside edge of the ion exit slit on the discharge cathode side and the rear edge of said arc discharge shaves the outside edge of the other end of said exit slit, whereby the stability of said arc discharge is subsTantially improved and the useable ion output of said source is increased.
 2. The calutron set forth in claim 1, wherein said means for slightly canting said magnetic field with respect to the direction of the elongated portion of said ion exit slit comprises positioning said ion source chamber and accelerating means at a small angle with respect to the direction of said magnetic field such that said small angle is provided between the direction of said elongated face portion of said slit and the magnetic field direction.
 3. The calutron set forth in claim 1, wherein said means for slightly canting the direction of said magnetic field with respect to the direction of the elongated face portion of said ion exit slit comprises providing a pair of spaced-apart magnetic shims between which said ion source chamber is mounted in spaced relation thereto, each of said shims having its face adjacent to said ion source cut at an angle such that said angled faces are parallel with respect to each other to provide a selected tilt to the direction of said magnetic field with respect to the direction of the elongated face portion of said ion source exit slit.
 4. The calutron set forth in claim 3, wherein said tilt is about one-fourth inch in 13 inches. 